The mystery behind yesterday’s emergency Go release is now explained. Go began blocking eight intermediate certificate authority keys without saying whose they were; Mozilla’s incident report and tracking page now confirm they belong to the Indian certificate authority eMudhra. A researcher known as Wayne found on 17 October that all eight certificates used P-384 private keys, generated in April 2025, with values smaller than 256. That means anyone could recover a key by testing 256 possibilities, then use it to sign forged certificates for any website. BleepingComputer reports that another researcher published one of the keys, whose value was just 4, and that it independently confirmed the published key matches one of the revoked certificates.
eMudhra told Mozilla that a bug in the script that generated the certificates created a second, weaker set of keys that was mistakenly picked for signing because the labels were similar to the correct ones. Some of the certificates were also cross-signed by Sectigo. The company says most of the intermediates were never used in production and it found no evidence of certificates issued to end users from them; BleepingComputer notes there is no evidence the keys were abused, though they could have been since April 2025. eMudhra has revoked all eight and stopped issuing under its G3 root.
Mozilla says it received the report on 17 October at 20:06 UTC and had blocked the certificates in Firefox through OneCRL, its revocation list, for standard configurations by 22:59 UTC that day, with no update needed. The eMudhra tracking page lists Chrome blocking them on 17 October, Apple devices on 19 October and Microsoft platforms on 20 October. Mozilla released Firefox 158.0.1 and ESR 115.43.1 and 153.5.1 on 20 October for users whose settings blocked the OneCRL update, and NSS 3.131.1 removes the root that signed the intermediates.
How to check if you’re affected
Affected products are mainly software that uses its own certificate bundle or does not check revocation, rather than mainstream browsers on default settings. BleepingComputer says such software may keep trusting the compromised intermediates until it is updated, and that macOS’s built-in /usr/bin/curl may still trust them because its bundle does not check revocation.
- Update Firefox to version 158.0.1 or later (ESR 115.43.1 / 153.5.1) if you changed settings that stop OneCRL updates.
- For servers, containers and developer tools, update the CA bundle or runtime your software relies on. Per the table BleepingComputer reproduced from Mozilla engineer Dennis Jackson’s tracking site, fixed versions at the time of writing include Go 1.27.3 / 1.26.10 (CVE-2026-111943), NSS 3.131.1, Python certifi 2026.10.19, the curl CA bundle dated 2026-10-20 and Alpine ca-certificates 20261020-r0; Debian, FreeBSD, Node.js and Bun were listed as pending. Check the tracking page for the current state of your platform.
- To test a command-line client, the tracking page says to run
curl https://dv-g3b-emudhra.we-have-a-problem.com/andcurl https://dv-g3b-aaa-emudhra.we-have-a-problem.com/; a certificate error means the client does not trust the compromised intermediates. It also offers the certificate chains for checking a trust store offline.
Sources
- Mozilla Security Blog: Protecting Firefox users following the compromise of eMudhra intermediate certificates
- Mozilla Bugzilla 2083449: Private key compromise of eMudhra Intermediate Certificates
- eMudhra Intermediate CA Compromise (incident tracking page)
- BleepingComputer: Mozilla, Google, Apple block compromised eMudhra CA certificates